Having the upper hand or dominance can be expressed in various ways. Some synonyms for the phrase "have the ascendancy" could be to have the advantage, hold sway, command the field, reign supreme, be in control, be on top, hold the whip hand, or be dominant. These phrases can be used in different contexts such as in sports, business, or in a personal relationship. It's important to use these phrases appropriately to convey the intended message accurately. Choosing the right synonym can also add more variety to one's vocabulary and make one's communication more interesting and engaging.